I've had the "theft system" problem for years with my 99 chevy malibu. I found this forum while searching for a solution to my problem- saw a solution, mulled it over for a few weeks, got stuck in parking lots in the 100 degree weather 3 times in one day, and the next day I did the fix.
Clipped the yellow wire with the car running, turned the car off, soldered a 3 dollar on/off switch from the Shack, left it in the "off" position, I've been a happy guy ever since.
The funny thing is, I heard on the radio just today a guy calling in with this exact problem. The shop guys immediately knew exactly what he was talking about and said, oh yeah, that's a GM thing, don't they have a recall on that yet, we see this all the time! Then they proceeded to recommend replacing the ingnition switch and lock cylinder. Now, I looked into doing that myself and it was about $300-350 so imagine what it would cost a shop to do it.
Anyway, point being, the swith thing works great. I've even turned the passlock system on and off to see if I did the wiring right- works like a charm. A million thanks to all who have help save me hundreds of dollars and the possible safety of my family.
As a side note, taking out the ignition assembly wasn't quite as easy as they say in the pictures posted in this thread. In the 99 Malibu LS there's a plastic bracket that lies between the ignition and the radio. I had to pull the radio out and the instrument panel as well to lift the ignition up and out. I've had to do this before so I was aware of the procedure- just thought I'd warn others who are wondering why they can't pull their ignition switch out through the radio slot.
Does this mean I'm also a member of the Anti-passlock Club too? Raycorri, you're my hero- really. Thanks.